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Reality check on K75S?

Just bought a '93 K75S, very clean and well kept with 23k miles on the clock. Overall seems to run well except that acceleration and throttle response seem a bit flat, and I notice significant roughness or engine vibration at full throttle at high rpm (above 6000 rpm or so), sort of a growly roughness as it revs above 6000 rpm at full throttle -- not overwhelming, but definitely there.

I should add that this is my second K75S, but I sold the first one some time ago so I'm not sure I'm remembering correctly. What I seem to remember is stronger acceleration than what I see on the new one, and I don't recall any kind of growly roughness at high rpm. Am I wrong about that? Is increased vibration common at high rpm under power? My other bike is a Japanese 4-cylinder naked bike that is fast and smooth all the way to redline, so perhaps I'm judging the K75S a bit harshly. But I really don't remember my former K75S being anything other than extremely smooth anywhere in the rpm range -- would appreciate a reality check on this.

If the rougness at high rpm is not normal, what could it be? I changed the plugs for good measure (originals looked past their prime, but no blatant signs of abnormality) and the engine starts easily and runs smoothly, it's only under hard acceleration that it seems a bit flat and a bit rough. I'm wondering if it could be the throttle bodies out of sync, or perhaps timing is off. I do notice that the fan comes on more often than I think it should, but I'm not quite sure what to expect. If I ride around residential streets in 2nd gear, 20 - 35 mph, temps from 70F to 85F the fan will go on and off -- is that as one would expect?

Any suggestions on what I'm seeing? How to check if there's a real problem or am just imagining things? How to diagnose or fix?

Is the fairing loose on your bike? Grab the front of the fairing below the headlight and try to pull it up and down. If the fairing is loose at the headstock you will feel a bunch of vibes at the top end.

Does your bike have heated grips? The hard rubber used in those seem to transfer a lot more vibes than the regular grips.

Regarding acceleration, are you sure you are opening the throttle all the way to the stop? Those bikes have a really long travel throttle and sometimes if the bike seems to flatten out, its because the grip isn't opened all the way.

Oh, and here's something you can't even do on a ZR-7, because it only has a five-digit odometer:

Originally posted by KBasa
That Kawasaki you have will kick the K75's behind in any kind of performance test. You've become acclimated to it, I fear.

Well, that's true, and I didn't expect the K75 would out-zip the Kawi, so was trying to gauge it vs. my former K75.

But in any case, the bigger concern is the roughness at high rpm. JDiaz asked about vibration via the fairing or grips, but it's engine roughness that I'm feeling and hearing, not the high-frequency buzz that indicates normal engine vibration. (The fairing is tight and I have gel grips, not heated grips.)

One thing my dad taught me about engines is that if they don't run right, always start by verifying that the ignition system is all up to standard, as it's generally the easiest thing to get both out of and into standard.
If that proves not to be the problem, I'd check that throttle sync- even if that isn't the problem either, you'll want to know that it's correct and if it is you'll reduce the number of different possible vibration sources that can be active at a time Most vibrations are rarely really *one* thing.

DR-The same thing happened to me going back to the K after spending 5-6K straight miles on the Triumph. No way can the K75 motor compete with the 955.
I second the opinion to get the ignition and TBs sussed out. My TBs usually manifested an Out of Sync by backfiring on partial throttle (>10%).
My last "rattle" or vibe was one of my storage boxes was loose. But you don't have those on your S.

Weirded out

I'm thoroughally intimidated by the picture!
A> if a passenger took it, how did they stay on
B> if not, you ARE crazier than me
C> how did it come out without blur
D> a HIGH speed spin tire balance test on centerstand?

Originally posted by DesertRider
Well, that's true, and I didn't expect the K75 would out-zip the Kawi, so was trying to gauge it vs. my former K75.

But in any case, the bigger concern is the roughness at high rpm. JDiaz asked about vibration via the fairing or grips, but it's engine roughness that I'm feeling and hearing, not the high-frequency buzz that indicates normal engine vibration. (The fairing is tight and I have gel grips, not heated grips.)

Thanks for any info or suggestions.

After spending time on other bikes, my K always felt much rougher at higher RPM's than I remembered. The reason was simple. You find yourself pushing the bike harder trying to find that spot where it might give the same thrill as that other bike.

As for general roughness, check the usual suspects...

1. FI system: is it gummed up at all? Those miles are very very few. That bike must have spent some time sitting. Sometimes it seems more like voodoo than a real solution, but try some quality FI cleaner.

2. valves

3. exhaust mounts. my old K developed a weird vibration that I tracked down to loose rear exhaust mounts (the bits hanging off the rear footpeg doohicky - if I remember correctly).

4. Airflow meter: Is the bike running at the proper 'richness'? You mention that the fan kicks on more often than you remember your old one. This one may be running a bit lean.

There is always a good chance that this bike is just fine. Different K's I rode had different levels of smoothness at different RPM's. Your old one may have felt smoother if only because it was more broken in.

Lastly, this K will always feel gutless compared to almost any other bike. It's a sad reality that helped drive me to a different bike. A lack of power when trying to pass someone on a mountain road gets old very fast.

I do miss that bike a wee bit. I miss the gentle quiet efficiency of the whole thing.

No joke guys

lancew & Custom Sarge,

You guys suffer from overactive imaginations. No tricks. Just an Olympus D-460 1.3Megapixel automatic point & shoot camera in my left hand. The red reflection is my helmet the white are clouds. Don't know how clouds could look like shop lights unless you are really in denial. We were crossing the desert in the early morning trying to beat the heat. My buddy here was right beside me on his K1100RS.